1. Field of the Invention
The invention disclosed in this specification and the like relates to a semiconductor device including transistors and further relates to a nitride insulating film included in the semiconductor device.
2. Description of the Related Art
In recent years, technical development on high-speed operation of semiconductor devices including central processing units (also referred to as CPUs) and the like has been actively conducted. CPUs include semiconductor integrated circuits including logic circuits. Semiconductor integrated circuits include transistors, memories, and electrodes serving as connection terminals, which are formed over semiconductor wafers.
As technical development on high-speed operation, semiconductor elements such as transistors are reduced in size to improve the operation speed and the degree of integration of CPUs.
By a reduction in size of a semiconductor element such a transistor, the degree of integration of a CPU is improved and the operation speed thereof is also improved; however, leakage current in the transistor is increased. As a result, the power consumption of the CPU is increased.
Semiconductor films which are applicable to transistors can be formed using not only widely known silicon semiconductors but also metal oxides exhibiting semiconductor characteristics (hereinafter referred to as oxide semiconductors).
For example, a technique for forming a transistor in which zinc oxide or an In—Ga—Zn-based oxide semiconductor is used as an oxide semiconductor in a channel formation region is disclosed (see Patent Documents 1 and 2).
In addition, a technique for manufacturing a highly integrated semiconductor device which consumes less power by being provided with a transistor using an oxide semiconductor over a transistor using a single crystal silicon semiconductor is disclosed (see Patent Document 3).